A bacterial biofilm is a community of bacteria (either single or multiple bacterial species) that adhere to a solid surface (Davey, M. E., et al., Microbiol Mol Biol Rev, 64:847–67 (2000)). In recent years, biofilms have received much attention due to their impact on industry and medicine. Biofilms are responsible for a plethora of problems ranging from biofouling of pipelines to facilitating tissue damage in Cystic Fibrosis patients (Barbeau, J., et al., Can J Microbiol, 44:1019–28 (1998)); Stickler, D., Curr Opin Microbiol, 2:270–5 (1999)); and Wen, Z. T., et al., Appl Environ Microbiol, 68:1196–203 (2002)).
Studies have clearly shown that a bacterial biofilm is not a result of random accretions of bacterial cells; rather, it is the net result of a community of bacteria cooperating to form well-differentiated structures (Costerton, J. W., et al., Annu Rev Microbial, 64:847–67 (2000)). The production of biofilm is dependent on the progression through several steps, from initial attachment to full maturity as a stable ecologic system (Pratt, L., et al., Curr Opin Microbiol, 2:598–603 (1999)). Given the tremendous metabolic and physiological changes that are required for the switch from planktonic to biofilm growth, it would seem reasonable that there exist some gene regulators responsible for facilitating this process. Indeed various gene regulation systems have been found to be involved in bacterial biofilm formation (Davies, D. G., et al., Science, 280:295–8 (1998)).
Quorum sensing is a mechanism for bacteria to change gene expression at very specific cell densities. To date, there are two types of recognized quorum sensing systems in bacteria. The first, known as intraspecies quorum systems, are species specific. In Gram-negative bacteria, intraspecies quorum signals are composed of an acyl-homoserine lactone backbone with species specific substitutions, while Gram-positive bacteria use various peptides as their signals (Dunny G. M., et al., Annu Rev Microbiol, 51:527–64 (1997); Fuqua, C., et al., Curr Opin Microbiol, 1:183–9 (1998); and Parsek, M. R., et al., Proc Natl Acad Sci USA, 97:8789–93 (2000)).
Recently, a second quorum sensing system was characterized in Vibrio harveyi. This system is referred to as the interspecies quorum system and is believed to operate as a universal quorum system for many bacteria possessing the characteristic luxS gene (Bassler, B. L., Curr Opin Microbiol, 2:582–7 (1999); Schauder, S., et al., Mol Microbiol, 41:463–76 (2001); and Surette, M. G., et al., Proc Natl Acad Sci USA, 96:1639–44 (1999)). The luxS gene is highly conserved among many species of Gram-negative and Gram-positive bacteria and is thought to be responsible for synthesizing a universally recognized quorum signal referred to as autoinducer-2 (AI-2) (Surette, M. G., et al., Proc Natl Acad Sci USA, 96:1639–44 (1999)). The chemical structure of the actual signal is still under investigation, however, crystallographic studies of the AI-2 receptor in Vibrio harveyi seem to suggest that AI-2 is a furanosyl borate diester formed from the metabolite 4,5-dihydroxy-2,3-pentadione (Chen, X., et al., Nature, 415:545–9 (2002); Ruzheinikov, S. N., et al., J Mol Biol, 313:111–22 (2001); and Schauder, S., et al., Mol Microbiol, 41:463–76 (2001)).
One feature regarding quorum sensing that has been extensively studied, is the link between intraspecies quorum sensing and biofilm related gene expression. There are several well-characterized examples for the involvement of intraspecies quorum sensing and biofilm formation. For example, lasI of Pseudomonas aeruginosa directs the synthesis of an acyl-homoserine lactone signal molecule used for P. aeruginosa intraspecies quorum signaling (Davies, D. G., et al. Science, 280:295–8 (1998)). Mutants in this gene were unable to produce biofilms that progressed beyond the very early stages of biofilm development (Davies, D. G., et al. Science, 280:295–8 (1998)). However, exogenous addition of the appropriate signal complemented the defect (Davies, D. G., et al. Science, 280:295–8 (1998)).
A similar result was also obtained due to inactivation of the cep intraspecies quorum sensing system of Burkholderia cepacia (Huber, B., et al., Microbiology, 147:2517–28 (2001)). Furthermore, a transposon mutagenesis study of the oral pathogen Streptococcus gordonii had detected a severe biofilm deficiency due to disruption of the two component system required for its intraspecies quorum sensing system (Loo, C. Y., et al., J Bacteriol, 182:1374–82 (2000)).
In Staphylococcus aureus, intraspecies quorum signaling has been implicated as a negative regulator of biofilm formation (Vuong, C., et al., J Infect Dis, 182:1688–93 (2000)). LuxS-dependent AI-2 signals have also been detected in a variety of bacterial species and found to be involved in various cellular processes in a cell density dependent manner (Day, W. A., Jr., et al., Infect Immun, 69:15–23 (2001); Forsyth, M. H., et al., Infect Immun, 68:3193–9 (2000); Frias, J., et al., Infect Immun, 69:3431–4 (2001); Joyce, E. A., et al., J Bacteriol, 182:3638–43 (2000); Lyon, W. R., et al., Mol Microbiol, 42:145–57 (2001); and Sperandio, V., et al., Proc Natl Acad Sci USA, 96:15196–201 (1999)).
S. mutans is a major cariogenic bacterium that normally inhabits a complex, multispecies, biofilm on the tooth surface (dental plaque) (Tanzer, J. M., et al., J Dent Educ, 65:1028–37 (2001)). The bacteria produce large amounts of exopolysacchrides, especially in the presence of sucrose, that enable them to adhere to the tooth.
The bacteria also have the ability to produce large amounts of acids from fermentable sugars in the diet. Acid accumulation can eventually dissolve the hard, crystalline structure of the tooth resulting in a carious lesion (Quivey, R. G., et al., Crit Rev Oral Biol Med, 12:301–14 (2001)). Previous studies have established some sophisticated interactions among the oral streptococci as well as with other oral bacteria within the same dental plaque (Kolenbrander, P. E., Enzymol, 253:385–97 (1995); Kolenbrander, P. E., Annu Rev Microbiol, 54:413–37 (2000); and Kolenbrander, P. E., et al., Infect Immun, 63:4584–8 (1995)).
There is a need in the art to develop methods and compositions useful for regulating biofilm formation, especially preventing or treating biofilm formation in association with microbial infections.